The peripheral edge part of a semiconductor wafer is conventionally polished by independently using a device for polishing the notch part (as disclosed in Japanese Patent Publication Tokkai 9-85599) and another device for polishing the beveled part (as disclosed in Japanese Patent Publications Tokkai 7-164301 and 8-174399). The polishing of the peripheral part is carried out by a so-called wet method whereby a polishing liquid in a slurry form obtained by dispersing abrading particles in water or a water-based reactive liquid is supplied to the target part to be polished (such as the notch and/or the beveled part) together with cooling water while a tape made of a woven or non-woven cloth or a foamed body or a tape having a polishing layer with abrading particles affixed by an adhesive formed on the surface of a plastic material is pressed onto the target part and caused to run.
Such conventional methods have problems because the notch and the beveled part of a semiconductor wafer are polished independently such that it takes too long to transport the wafer between these two devices and this requires a large space for the equipment. There is also the problem of the semiconductor wafer becoming dry while being transported, adversely affecting the yield of device wafers.
The positioning of a semiconductor wafer on the wafer stage in each polishing device is carried out by means of a pair of chuck handles of a robot for transporting wafers but since a plurality of cylinders are used for improved accuracy in the positioning, a large space is required for the equipment. Since air cylinders are used for the purpose, furthermore, an error on the order of 0.5 mm arises in the positioning. There is still another problem that an excessive grasping force is applied on the peripheral edge of the wafer and tends to damage the edge portion of the wafer.
The semiconductor wafer is adsorbed to the wafer stage by vacuum. When this semiconductor wafer is removed from the wafer stage, the wafer is released from this condition of vacuum adsorption as the wafer is grasped on its peripheral parts by the pair of chuck handles of the robot and lifted up. This means that a large releasing force is required for removing the semiconductor wafer from the wafer stage and this must be exerted instantaneously on the semiconductor wafer. This gives rise to the problem of deforming or damaging the semiconductor wafer.
According to prior art technologies, a polishing tape is supplied from a supply roller during the polishing process by changing the torque value of a motor for the supply of the tape according to the outer diameter of the tape (that is, the amount of the tape still remaining on the supply roll) such that the tension of the tape pressed onto the target portion to be polished can be adjusted. Since the outer diameter of the tape is determined by the presence or absence of light from a light emitter received by a plurality (usually eight) of sensors of a light receiving part arranged at the side of the tape supply roll, the torque value of the motor changes in a stepwise manner, giving rise to the problem of the tension in the tape not being constant.